Method and radio node for handling CSI reporting

ABSTRACT

Separate aperiodic channel state information (CSI) reports are handled for static subframe(s), in which the direction of signal transmission is fixed, and flexible subframe(s), in which the direction of signal transmission is variable. A method by a UE includes receiving a trigger for an aperiodic CSI report as part of an uplink (UL) grant from a radio node in a static downlink (DL) subframe, where the trigger indicates a CSI subframe set, out of at least two alternative CSI subframe sets. An aperiodic CSI measurement is performed for a CSI reference resource in the indicated CSI subframe set, and the result of the CSI measurement is reported to the radio node. One of the at least two alternative CSI subframe sets relates to the one or more static subframes, and another one of the at least two alternative CSI subframe sets relates to the one or more flexible subframes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/910,611, filed Feb. 5, 2016, which is a national stage applicationunder 35 U.S.C. § 371 of PCT International Application No.PCT/SE2014/050942, filed on Aug. 15, 2014, which itself is acontinuation of PCT International Application No. PCT/CN2013/081556,filed Aug. 15, 2013, the disclosure and content of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to Channel State Information,CSI, reporting in wireless communication networks, and in particular tomethods in a radio node and a User Equipment (UE) and correspondingradio node and UE for handling aperiodic CSI reporting separately forflexible and static subframes.

BACKGROUND

In the field of radio communication in cellular networks, the term “UserEquipment, UE” is commonly used and will be used in this disclosure torepresent any user-controlled wireless terminal, mobile phone, tablet ordevice capable of radio communication including receiving downlinksignals transmitted from a radio node and sending uplink signals to theradio node. Further, the term “radio node”, also commonly referred to asa base station, e-nodeB, eNB, etc., represents any node of a wirelesscellular network that can communicate uplink and downlink radio signalswith UEs. The radio nodes described here may, without limitation,include so-called macro nodes and low power nodes such as micro, pico,femto, Wifi and relay nodes, to mention some customary examples.Throughout this disclosure, the term “BS” or “eNB” is often used todenote a radio node.

In a cellular network for radio communication, a Time Division Duplex(TDD) configuration of subframes may be used for uplink and downlinktransmissions in cells where consecutive subframes are comprised in arepeatable radio frame. The subframes are reserved for uplinktransmissions from User Equipments (UEs) to a serving radio node and fordownlink transmissions from the radio node to the UEs such that uplinkand downlink transmissions do not occur at the same time within thecell. A subframe is basically defined by a preset time period of acertain length, typically 1 millisecond (ms), and each subframe maycomprise two time slots of 0.5 ms each. Further, a radio frame comprisesa predefined number of consecutive subframes, e.g. ten subframes. Insuch a network, different radio nodes are able to use differentconfigurations of subframes, e.g. depending on the current need foruplink and downlink radio resources, respectively.

An example of different TDD configurations that can be used by radionodes in different cells is shown in the table of FIG. 1 comprisingseven different TDD configurations 0-6 each having ten subframes 0-9including downlink subframes “D”, uplink subframes “U” and so-calledspecial subframes “S”. The special subframes S are configured with onepart reserved for downlink, another part reserved for uplink, and aguard period between the two parts allowing neither uplink nor downlink.It can be seen in this example that the first three subframes 0-2 andsubframe 5 are reserved for downlink D, special S, uplink U, anddownlink D, respectively, in all TDD configurations 0-6, while theremaining subframes 3, 4, 6-9 can vary in different TDD configurations.The latter subframes 3, 4, 6-9 may be referred to as flexible subframeshaving a variable link direction, and the former subframes 0-2 and 5 maybe referred to as static or fixed subframes having a fixed linkdirection.

In this disclosure, the term “flexible subframe” thus denotes a subframein which the direction of transmission, i.e. downlink or uplink, maydiffer between different cells so that the flexible subframe may be usedfor downlink transmission in one cell and for uplink transmission inanother cell. Further, a flexible subframe may differ from one radioframe to another in the same cell so that the flexible subframe is usedin the cell for downlink in one radio frame and for uplink in anotherradio frame. Thereby, transmissions in flexible subframes may, at leastin some radio frames, cause interference between different neighboringcells as follows. In this disclosure, the expression “during a flexiblesubframe” should be understood as in the flexible subframe or in asubframe that overlaps in time with the flexible subframe depending onif the UE is served by the radio node that applies the subframe schemewith the flexible subframe or if the UE is served by a neighboring radionode that applies a subframe scheme with a subframe that overlaps orcoincides in time with the flexible subframe.

When different TDD configurations are used in two neighboring cells,interference may occur across the cells during a flexible subframe wheredownlink is permitted in one cell and uplink is permitted in the othercell at the same time. In this description, the term “neighboring cells”means that they are close enough to one another so that transmissions inone cell can potentially cause interference in the other cell.

Interference due to different TDD configurations in neighboring cellscan be either 1) downlink to uplink interference when a downlinktransmission from a radio node of one cell disturbs an uplink receptionin a radio node of the other cell during a flexible subframe, or 2)uplink to downlink interference when an uplink transmission from a UE inone cell disturbs a downlink reception in a UE in the other cell duringa flexible subframe. Of these two scenarios, 1) refers to interferencebetween radio nodes which is more or less predictable and thisinterference can be controlled quite accurately since the radio nodes inthe neighboring cells are in fixed positions relatively far away fromeach other such that the downlink signals from one radio node are notvery strong when received in the other radio node.

On the other hand, scenario 2) above refers to interference between UEswhich is more unpredictable since the UEs move around and may sometimesbe located quite near each other while being served by different radionodes, e.g. when both are located close to the borders of theirrespective cells. This scenario is illustrated in FIG. 2 where a firstUE denoted “UE1” is located near the border of a first cell 1 served bya first radio node “BS1” using a TDD configuration allowing the UE1 totransmit uplink signals “UL1” in a certain subframe. At the same time, asecond UE “UE2” is located near the border of a second cell 2 served bya second radio node “BS2” using another TDD configuration allowing UE2to receive downlink signals “DL2” in the same subframe, thus being aflexible subframe in this context. Since UE1 and UE2 happen to be quiteclose to one another but relatively far away from their respective radionodes, the uplink signals UL1 transmitted with high power from UE1 willinterfere strongly with the relatively weak downlink signals DL2received by UE2 during the flexible subframe. This UE to UE interference“I” is illustrated by a dashed arrow.

FIG. 3A shows two examples of TDD configurations which can cause UE toUE interference across neighboring cells 1 and 2. In cell 1, TDDconfiguration 1 of FIG. 1 is used and in cell 2, TDD configuration 2 ofFIG. 1 is used. It can be seen in both of FIG. 1 and FIG. 3A thatflexible subframes 3 and 8 are configured differently in the two cellssuch that they are uplink subframes in cell 1 and downlink subframes incell 2, hence potentially causing UE to UE interference I from cell 1 tocell 2, illustrated by dashed arrows in FIG. 3A. In this case, UE1 canbe called an “aggressor UE” and UE2 can be called a “victim UE”.Likewise, cells 1 and 2 can be called “aggressor cell” and “victimcell”, respectively. It is thus a problem that, in a radio communicationnetwork allowing different TDD configurations with one or more flexiblesubframes in different cells, downlink radio signals received by avictim UE in a victim cell during a flexible subframe, may be subjectedto interference caused by an uplink transmission from an aggressor UE inan aggressor cell during that subframe, e.g. depending on the relativedistance and locations of the UEs which are typically unpredictable.

In wireless communications, Channel State Information, CSI, refers tochannel properties of a radio communication link. This informationbasically describes how a signal propagates from the transmitter to thereceiver. The CSI makes it possible to adapt transmissions to currentchannel conditions, which may be helpful for achieving reliablecommunication with high data rates in a cellular network. The CSI needsto be estimated at the receiver, typically the UE, and it is usuallyquantized and reported back to the transmitter, typically the radio nodeserving the UE. This report is commonly referred to as CSI feedback. ACSI report may comprise a Channel Quality Indicator, CQI, a PrecodingMatrix Indicator, PMI and/or a Rank Indicator, RI.

CSI feedback is typically used to support the performance of a wirelessaccess network in various respects. For example, it is commonly used asa basis for different RRM functionalities such as scheduling, linkadaptation as well as interference coordination. It can also be used forrank and precoding matrix recommendations for MIMO transmission. In LTE,two CSI reporting schemes are supported: periodic CSI reporting andaperiodic CSI reporting. The following disclosure relates to aperiodicCSI reporting for a TDD system where fast or flexible UL/DLreconfigurations are employed.

It is expected that wireless data traffic will become more and morelocalized in the future, where most UE users will be in hotspots, or inindoor areas, or in residential areas. These UE users will thustypically be located in clusters within a limited area of a cell servedby a radio node, and the UEs will produce different UL and DL traffic atdifferent times to and from the radio node, respectively. Thisessentially means that a dynamic feature to adjust the UL and DLresources to instantaneous (or short term) traffic variations would berequired in future local area cells. In this case, a TDD system whichhas the flexibility to dynamically allocate the UL/DL resourcesdepending on current traffic situation becomes very attractive.

As described above, today, there are seven different TDD UL/DLconfigurations defined in LTE, shown in the table of FIG. 1, providing arange of 40%-90% resources for DL. It can be seen in FIG. 1 that forexample TDD configuration 5 has much more resources for DL than, say,TDD configuration 0. In current specification, the UL/DL configurationis semi-statically configured, thus it may not well match theinstantaneous traffic situation which may vary quite rapidly. Faster TDDreconfigurations, hereafter referred to as “dynamic TDD”, have showngood performance potentials in both UL and DL, especially at low tomedium system load, and dynamic TDD will become a standardized featureof LTE Rel-12. It should be noted that more TDD configurations than theones listed in the table in FIG. 1 may be introduced in the future. Theherein suggested solution is not limited to the existing TDDconfigurations; rather it is equally applicable to new configurationsdefined in future.

Different signaling methods are being considered to support dynamic TDDreconfigurations with different time scale. Theoretically, each subframecould be allocated as either UL or DL. However, this would pose bigchallenges to operations like DL/UL switching, random access, radio linkmonitoring, handover, etc. Moreover, it would be virtually impossible toachieve backward compatibility with legacy UEs. Therefore, it is morepractical to dynamically change between UL and DL among a subset of thesubframes, e.g. by changing between the different TDD configurations inFIG. 1. In this case, the subframes can be divided into two types:static subframes and flexible subframes. The static subframes have fixedlink directions for all TDD configurations, while flexible subframes canbe either UL or DL in different TDD configurations, and can thereby bedynamically changed between UL and DL, e.g. by change of TDDconfiguration for a cell, as described above.

It may be up to the eNB to configure the set of flexible subframesdepending on the traffic situation. One possible way is to signal twodifferent UL/DL TDD configurations to a UE, such that the flexiblesubframes are determined implicitly by the two reference TDDconfigurations i.e., as said above, the subframes in which the linkdirections in the two TDD configurations may be different are defined asflexible subframes. FIG. 3B shows an example where reference TDDconfiguration 0 is used for UL and reference TDD configuration 2 is usedfor DL. In this example, the static downlink subframes, which mayinclude normal subframes and special subframes, are subframes 0, 1, 5and 6, while the static uplink subframes are subframe 2 and 7, thesubframes 0-2 and 5-7 thus being static subframes with fixed linkdirections. The remaining subframes 3, 4, 8 and 9 are flexible subframeswhich can be used for either uplink or downlink transmissions.

Considering UE reception in the two types of subframes, the interferencesituations may be different in different subframes, e.g. as describedabove with reference to FIGS. 1-3B. In static DL subframes, theinter-cell interference is generated by neighboring eNB(s), while inflexible subframes the inter-cell interference could either be generatedby neighboring eNB(s) or by certain UE(s) served by the neighboringeNB(s) which are currently scheduled for UL transmissions. To deal withthe above different interference situations, separate CSI measurementsshould be employed for the two types of subframes so that DL schedulingas well as link adaptation can be properly performed for both types ofsubframes on the basis of the respective CSI measurements. Thus, thereis a need for mechanisms for handling such separate CSI measurements.

SUMMARY

It is desirable to find methods for handling separate CSI measurementsfor static and flexible subframes. In this disclosure, a solution isdescribed for triggering a UE to perform aperiodic CSI reporting forstatic downlink subframes and for flexible downlink subframesseparately. This is achieved by methods and nodes as described in theappended independent claims. The solution is robust, easy to implementand introduces very little overhead, and further has low impact oncurrent standardization, e.g. minimizing need for changes.

According to a first aspect, a method is provided, to be performed by aUE, for handling separate aperiodic CSI reports for one or more staticsubframes, in which the direction of signal transmission is fixed, andone or more flexible subframes, in which the direction of signaltransmission is variable. The method comprises receiving a trigger foran aperiodic CSI report as part of an UL grant from a radio node in astatic DL subframe. The trigger indicates a CSI subframe set, out of atleast two alternative CSI subframe sets. One of the at least twoalternative CSI subframe sets relates to the one or more staticsubframes, and another one of the at least two alternative CSI subframesets relates to the one or more flexible subframes. The method furthercomprises performing an aperiodic CSI measurement for a CSI referenceresource in the indicated CSI subframe set, and, reporting a result ofthe CSI measurement to the radio node. The result of the CSI measurementmay be reported to the radio node in a CSI reporting subframe n.

According to a second aspect, a method is provided to be performed by aradio node for handling separate aperiodic CSI reports for one or morestatic subframes, in which the direction of signal transmission isfixed, and one or more flexible subframes, in which the direction ofsignal transmission is variable. The method comprises indicating to aUE, in an UL grant in a static DL subframe, a CSI subframe set, out ofat least two alternative CSI subframe sets, in which the UE shouldperform an aperiodic CSI measurement for a CSI reference resource. Oneof the at least two alternative CSI subframe sets relates to the one ormore static subframes, and another one of the at least two alternativeCSI subframe sets relates to the one or more flexible subframes. Themethod further comprises receiving a CSI report from the UE comprising aresult of the CSI measurement in the indicated CSI subframe set. Thereport may be received in a CSI reporting subframe n.

According to a third aspect, a UE is provided for handling separateaperiodic CSI reports for one or more static subframes, in which thedirection of signal transmission is fixed, and one or more flexiblesubframes, in which the direction of signal transmission is variable.The UE is configured to receive a trigger for an aperiodic CSI report aspart of an UL grant from a radio node in a static DL subframe. Thetrigger indicates a CSI subframe set, out of at least two alternativeCSI subframe sets. One of the at least two alternative CSI subframe setsrelates to the one or more static subframes, and another one of the atleast two alternative CSI subframe sets relates to the one or moreflexible subframes. The UE is further configured to perform an aperiodicCSI measurement for a CSI reference resource in the indicated CSIsubframe set, and to report a result of the CSI measurement to the radionode. The UE may be configured to report the result of the CSImeasurement to the radio node in a CSI reporting subframe n.

According to a fourth aspect, a radio node is provided for handlingseparate aperiodic CSI reports for one or more static subframes, inwhich the direction of signal transmission is fixed, and one or moreflexible subframes, in which the direction of signal transmission isvariable. The radio node is configured to indicate to a UE, in an ULgrant in a static DL subframe, a CSI subframe set, out of at least twoalternative CSI subframe sets, in which the UE should perform anaperiodic CSI measurement for a CSI reference resource. One of the atleast two alternative CSI subframe sets relates to the one or morestatic subframes, and another one of the at least two alternative CSIsubframe sets relates to the one or more flexible subframes. The radionode is further configured to receive a CSI report from the UEcomprising a result of the CSI measurement in the indicated CSI subframeset. The radio node may be configured to receive the CSI report from theUE in a CSI reporting subframe n.

According to a fifth aspect, a use of at least one bit in a CSI requestfield in an UL grant on a PDCCH or ePDCCH is provided for indicating oneof a plurality of different CSI subframe sets to a wireless device,characterized in that one of the plurality of different CSI subframesets relates to one or more static subframes, and another one of theplurality of different CSI subframe sets relates to one or more flexiblesubframes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by means ofexemplifying embodiments and with reference to the accompanyingdrawings, in which:

FIG. 1 shows different TDD configurations in LTE.

FIG. 2 shows an exemplifying scenario where interference due to dynamicTDD with different TDD configurations in neighboring cells may occur.

FIG. 3A shows two different TDD configurations, and the possibleinterference which may occur when used simultaneously in neighboringcells.

FIG. 3B shows a frame structure of dynamic TDD for UL referenceconfiguration 0 and DL reference configuration 2.

FIG. 4 is a flow chart illustrating a method to be performed by a UE,according to an exemplifying embodiment.

FIG. 5 is a flowchart illustrating a method to be performed by a radionode according to an exemplifying embodiment.

FIGS. 6 and 7 are block schemes illustrating possible implementations ofa UE according to exemplifying embodiments.

FIGS. 8 and 9 are block schemes illustrating possible implementations ofa radio node according to exemplifying embodiments.

DETAILED DESCRIPTION

In prior art specification, an aperiodic CSI report is triggered byuplink grants (DCI format 0/4) carried by a Physical Downlink ControlChannel, PDCCH, or an Evolved PDCCH, E-PDCCH. If an aperiodic CSI reportis triggered in subframe n, a UE shall perform CSI measurements on animplicit CSI reference resource and perform aperiodic CSI reportingusing a Physical Uplink Shared CHannel, PUSCH, in subframe n+k, where kis the scheduling timing delay for PUSCH. The CSI is determined for agroup of downlink physical resources denoted “CSI reference resource” in3GPP. For aperiodic CSI reporting, the CSI reference resourcecorresponds, in the time domain, to the subframe of the correspondingCSI request. That is, the CSI reference resource is implicitly decidedby the subframe in which the request for an aperiodic CSI report wassent. In dynamic TDD, UL transmissions in both static subframes andflexible subframes are scheduled by the UL grants sent in static DLsubframes. The inventors have realized that there are problems with thecurrent specified request mechanisms for aperiodic CSI schemes fordynamic TDD deployment when the aperiodic CSI measurement and reportmade by the UE for the static and the flexible downlink subframes shouldbe requested separately.

The reason for transmitting UL grants in static DL subframes is toenable backwards compatibility, and to avoid introduction of new ULscheduling and HARQ timing designs which would entail substantialadditional complexity to both eNB and UE. By backwards compatibility ismeant e.g. that any UE, irrespective of which DL TDD configuration thatis used, should be able to receive the UL grant. Thus, since in priorart the CSI reference resource depends on, and for the time domain infact is, the DL subframe in which the aperiodic CSI was triggered, itwill always be in the same type of subframe, namely a static subframe.This is not compatible with the need to request aperiodic CSI also forflexible subframes, as realized by the inventors.

The inventors have realized that a solution is needed for enablingaperiodic CSI requests for both static and flexible subframes,respectively. It is desirable that this solution introduces as littleoverhead as possible, is easy to implement, and that it is furtherfavorable if the solution entails a minimum of changes to the currentstandards.

According to the prior art, there is a possibility to trigger aperiodicCSI reports for different carriers and for different CSI processes. Thepossibility to trigger a CSI report for different carriers is related toCarrier Aggregation, CA, where a UE may be configured with a number ofdifferent carriers, on different radio frequencies, which may requiredifferent CSI reporting. The alternative to trigger aperiodic CSIreports for different CSI processes is related to a technique referredto as “Coordinated MultiPoint, CoMP, transmission and reception”. A CSIprocess could be explained as follows: A transmission hypothesis in CoMPis composed of two parts: signal hypothesis and interference hypothesis.The signal hypothesis specifies transmission point(s), TP(s), from whichdata is assumed to be transmitted, and the interference hypothesisstands for interference suffered during the assumed data transmission.CSI corresponding to one transmission hypothesis is defined as a CSIprocess. A CSI process is determined by the association of a signalhypothesis and an interference hypothesis, where the signal hypothesisand interference hypothesis are measured through or on CSI-RS andinterference measurement resource (IMR), respectively. However, this isnot related to different subframe sets comprising either static orflexible subframes.

The inventors have realized that in order to enable separate requestingor triggering of aperiodic CSI reports for static and flexible subframesrespectively, a new scheme to address different types of subframes isneeded. Below, such a scheme will be described with reference toillustrative drawings. The solution will first be described from theperspective of a UE, and then from the perspective of a radio node, BSor eNB.

In the following description, triggering a UE to perform aperiodic CSIreporting is sometimes referred to e.g. as a “CSI request” or a “CSIreport request”.

Method for User Equipment, UE

Examples of embodiments of a method performed by a UE, for handlingseparate aperiodic CSI reports for one or more static subframes, inwhich the direction of signal transmission is fixed, and one or moreflexible subframes, in which the direction of signal transmission isvariable, will now be described with reference to a flowchart depictedin FIG. 4. The UE is configured to be operable in a wirelesscommunication system applying dynamic TDD. The method comprises thefollowing actions, which actions may be taken in any suitable order.

Action 401

The UE receives a trigger for an aperiodic CSI report as part of anuplink, UL, grant from a radio node, e.g. a BS, in a static DL subframe.The trigger indicates a CSI subframe set, out of at least twoalternative CSI subframe sets. One of the at least two alternative CSIsubframe sets relates to the one or more static subframes, and anotherone of the at least two alternative CSI subframe sets relates to the oneor more flexible subframes.

The UL grant, gives permission to the UE to transmit in an UL subframe.The UL grant may be sent in downlink control information, DCI. The term“UL grant” is here considered to encompass also Random Access grants.The received UL grant comprises, in a CSI request field, one or morebits indicating the CSI subframe set. The indicated CSI subframe set mayrefer to or comprise the one or more static subframes, or, the indicatedCSI subframe set may refer to or comprise the one or more flexiblesubframes. For example, when the trigger or indicator comprises two bitswith the value “01” this may be defined to indicate that an aperiodicCSI report is requested for the one or more flexible subframes.Correspondingly, when the two bits have the value “11”, this may bedefined to indicate that an aperiodic CSI report is requested for theone or more static subframes. The trigger may further take on othervalues, e.g. “00”, which may be defined to indicate that no aperiodicCSI report is requested at this time. The bits in the CSI request fieldmay thus be seen as a trigger that indicates a CSI subframe set forwhich an aperiodic CSI report is requested. The indication or triggermay be received e.g. over a PDCCH or an E-PDCCH.

In some embodiments, the trigger may further indicate one or more CSIprocesses.

Action 402

This action may be regarded as implicitly included e.g. in action 403(and therefore have a dashed outline), but is shown in FIG. 4 tofacilitate understanding. When the trigger is received, the triggerneeds to be decoded, i.e. the UE needs to determine which type of CSIsubframe set that is indicated by the trigger, i.e. if the one or moresubframes in the indicated CSI subframe set are flexible or static. Thiscould alternatively be expressed as that the UE needs to determine whichtrigger, out of a plurality of triggers, that was comprised in the ULgrant.

Action 403

The UE performs an aperiodic CSI measurement for a CSI referenceresource in the indicated CSI subframe set.

When the trigger indicates, or is determined to indicate, a set ofstatic subframes, i.e. the one or more static subframes, as the CSIsubframe set, the CSI measurement will be performed for at least one CSIreference resource in the set of static subframes. Correspondingly, whenthe trigger indicates, or is determined to indicate, a set of flexiblesubframes, i.e. the one or more flexible subframes, as the CSI subframeset, the CSI measurement will be performed for at least one CSIreference resource in the set of flexible subframes. The CSI measurementneed not be performed on the exact resources defined as the CSIreference resource, but could be performed on radio resourcescorresponding to or representing the CSI reference resource. In otherwords, the CSI measurement should represent a measurement performed onthe CSI reference resource. The CSI reference resources for thedifferent CSI subframe sets could be predefined, such that both the UEreceiving the indication or trigger and the radio node sending theindication or trigger agree on, i.e. have a common understanding on,which resources that are the CSI reference resource for each respectiveCSI subframe set. The UE and radio node should further agree on thedefinition of the trigger, which could also be predefined. Thisinformation on trigger and CSI reference resources could be provided tothe UE and/or radio node as part of a setup procedure, and/or e.g. beotherwise communicated or updated from a management node to the radionode and from the radio node to the UE, e.g. via RRC signaling. How theCSI reference resource may be defined will be described in more detailfurther below.

Action 404

The UE reports a result of the CSI measurement to the radio node.

The CSI measurement result is processed by the UE, and the result ispresented to the radio node in an aperiodic CSI report. The report istransmitted in an UL subframe, which may be defined by the trigger, orbe implicitly linked to the subframe in which the aperiodic CSI reportwas triggered. For example, the report may be transmitted in a CSIreporting subframe n, where n is a subframe index.

In some embodiments, when the indicated CSI subframe set relates to theone or more flexible subframes, the CSI reference resource is defined,in the time domain, as a single downlink subframe n-n_(CQI) _(_) _(ref),where n_(CQI) _(_) _(ref) is an offset such that the single downlinksubframe is a valid downlink subframe belonging to the indicated CSIsubframe set, and where n is the subframe index for the CSI reportingsubframe.

Method for Radio Node, e.g. BS

Embodiments of the method will now be described seen from theperspective of a radio node, e.g. a BS. The radio node or BS could insome embodiments be an eNB. Thus, examples of embodiments of a methodperformed by a radio node for handling separate aperiodic CSI reportsfor one or more static subframes, in which the direction of signaltransmission is fixed, and one or more flexible subframes, in which thedirection of signal transmission is variable will now be described withreference to a flowchart depicted in FIG. 5. The method comprises thefollowing actions, which may be performed in any suitable order:

Action 501

This action may be considered to be implicitly included e.g. in action503, but is schematically illustrated here to facilitate understanding.For this reason the action is outlined with a dashed line. The actioncould be described as the radio node determines whether there is a needfor an aperiodic CSI report from a UE. When there is, an aperiodic CSIreport request is to be transmitted to the UE as part of DL controlinformation, as previously described.

Action 502

As for action 501, this action may also be considered to be implicitlyincluded in action 503 or in action 501. The action could be describedas to determine whether an aperiodic CSI report is needed for flexiblesubframes/resources or for static subframes/resources. This could bedetermined in association with determining the possible need forrequesting an aperiodic CSI report e.g. in action 501.

Action 503

The radio node indicates to a UE, in an UL grant in a static DLsubframe, a CSI subframe set, out of at least two alternative CSIsubframe sets, in or upon which the UE should perform CSI measurementsfor a CSI reference resource, where one of the at least two alternativeCSI subframe sets relates to, e.g. refers to or comprises, the one ormore static subframes, and another one of the at least two alternativeCSI subframe sets relates to, e.g. refers to or comprises, the one ormore flexible subframes.

When it is clear that there is a need for an aperiodic CSI report for acertain type of subframe, flexible or static, a request for such areport is to be signaled from the radio node to the UE. That is, such areport should be triggered by the radio node. The action couldalternatively be formulated as that a report is requested by use of anindicator or trigger. The indicator, or trigger, comprises at least onebit, and different values of the at least one bit, such as “01”, “10” or“11” may be referred to as different triggers indicating different CSIsubframe sets, e.g. the one or more static subframes or the one or moreflexible subframes, and being linked to different CSI referenceresources depending on what CSI subframe set is indicated.

In some embodiments the indicating may further comprise indicating oneor more CSI processes to the UE.

Action 504

The radio node receives a CSI report from the UE in the indicated CSIsubframe set. The CSI report comprises a result of the aperiodic CSImeasurement.

The CSI report is received in response to the aperiodic CSI reportrequest comprising the indication or trigger as described above. Whenthe trigger indicates a CSI subframe set of flexible subframes, the CSIreport will relate to a CSI reference resource in one or more flexiblesubframes. Correspondingly, when the trigger indicates a CSI subframeset of static subframes, the CSI report will relate to a CSI referenceresource in one or more static subframes. The CSI report is received inan UL subframe n, which may be implicitly known and depend on thesubframe in which the CSI report was requested. The UL subframe n isthus the CSI reporting subframe where the CSI report that comprises theresult of the aperiodic CSI measurement indicated by the CSI subframeset is received at the radio node.

In some embodiments, when the indicated CSI subframe set relates to theone or more flexible subframes, the CSI reference resource is defined,in the time domain, as a single downlink subframe n-n_(CQI) _(_) _(ref),where n_(CQI) _(_) _(ref) is an offset such that the single downlinksubframe is a valid downlink subframe belonging to the indicated CSIsubframe set, and where n is the subframe index for the CSI reportingsubframe.

CSI Reference Resources

When the UE receives a trigger for an aperiodic CSI measurement andreport according to the above, the UE should measure a signalrepresenting or corresponding to a signal transmitted on a CSI referenceresource, e.g. in terms of channel measurement and/or interferencemeasurement, and further determine a CSI from the measurement. The CSIreference resource is a frequency-time resource for which the UE shoulddetermine CSI. The CSI is then reported to the radio node and used bythe radio node e.g. for scheduling in corresponding resources, aspreviously described.

In an exemplifying embodiment of the method described above, the CSIreference resource for the flexible subframes, i.e. the flexiblesubframe set, may be defined as follows:

-   -   In the time domain, the CSI reference resource may be defined        e.g. as a single downlink subframe n-n_(CQI) _(_) _(ref) where        n_(CQI) _(_) _(ref) is the time offset between the CSI reporting        subframe n, and the single downlink subframe, also denoted CSI        reference resource subframe,        -   where n_(CQI) _(_) _(ref) should be such that the CSI            reference resource is in a valid downlink subframe belonging            to the set of flexible subframes. n_(CQI) _(_) _(ref) may be            configured, and thus known to the UE and radio node, as part            of a setup procedure, and/or be provided or updated as part            of control signaling, e.g. RRC signaling,    -   In the frequency domain, the CSI reference resource may be        defined as the group of downlink physical resource blocks        corresponding to the band to which a derived CQI value relates.

By “valid downlink subframe” is meant a subframe which is scheduled fordownlink communication or at least configured for downlinkcommunication.

In the embodiments above, one or more bits may be added in downlinkcontrol information, DCI, to trigger the UE to perform CSI measurementsand deliver an aperiodic CSI report for a fixed, i.e. static, subframeor for a flexible subframe. Alternatively, one or more existing bits inDCI may be used to trigger the UE to perform CSI measurements anddeliver an aperiodic CSI report for a fixed, i.e. static, subframe orfor a flexible subframe. For example, when an added or existing bit inthe DCI is set to 1 (or 0) it may be a trigger for an aperiodic CSIreport for a fixed, i.e. static, subframe, and when this bit in the DCIis set to 0 (or 1) it may be a trigger for an aperiodic CSI report for aflexible subframe. A combination of one or more existing bits and one ormore added bits may also be used for triggering different aperiodic CSIreports.

In case of carrier aggregation, when a UE is associated with at leasttwo carriers, the aperiodic CSI request field in UL grants comprises twobits. Similarly, for UEs applying CoMP, which are configured with aplurality of CSI processes, the aperiodic CSI request field, or CSIinformation field, in UL grants comprises two bits. However, for UEsconfigured with one carrier and only one CSI process, the aperiodic CSIrequest field in UL grants comprises only one bit. For such singlecarrier, single CSI process UEs, the aperiodic CSI request field couldbe updated to comprise more than one bit, e.g. two bits. For UEs wherethe aperiodic CSI request field already comprises more than one bit,these bits could be re-used and redefined.

Some potential advantages that may be achieved by implementing thesolution according to any of the above-described embodiments includeimproved performance and/or capacity in the cellular network since UEsare enabled to provide more accurate and useful CSI reports when dynamicTDD with both static and flexible subframes is employed. The UEs can betriggered to perform the CSI reporting in a simple manner and with aminimum of signaling overhead. Implementing the solution will also havevery low impact on the standard, e.g. minimizing standard changes.

Embodiments of Nodes

Below, implementations of a UE and a radio node, e.g. BS, will bedescribed with reference to FIGS. 6-9. The UE and radio node areconfigured to perform at least a respective one of the methods describedabove with reference to FIGS. 4-5. The nodes will be described in briefin order to avoid unnecessary repetition.

User Equipment, UE

Embodiments described herein also relate to a UE, operable in a wirelesscommunication system. The UE is configured to perform at least oneembodiment of the method performed by a UE described above. The UE isassociated with the same technical features, objects and advantages asthe method described above and illustrated e.g. with reference to FIG.4.

Below, an exemplifying UE 600, configured to enable the performance ofan above described method for handling separate aperiodic CSI reportsfor one or more static subframes, in which the direction of signaltransmission is fixed, and one or more flexible subframes, in which thedirection of signal transmission is flexible, will be described withreference to FIG. 6. The UE 600 is configured to be operable in awireless communication network and can thus be assumed to be operablee.g. to communicate with a radio node serving the UE and to performmeasurements related to radio signals. The part of the UE 600 which ismost affected by the adaptation to the herein described method isillustrated as an arrangement 601, surrounded by a dashed line. The UE600 and arrangement 601 are further configured to communicate with otherentities via a communication unit 602 comprising means for wirelesscommunication. The UE 600 or arrangement 601 may be assumed to comprisefurther functionality 606, for carrying out regular UE functions.

The arrangement part of the UE may be implemented and/or described asfollows: The arrangement 601 comprises processing means 603, such as aprocessor, and a memory 604 for storing instructions, the memorycomprising instructions, e.g. computer program 605, which when executedby the processing means causes the UE 600 or arrangement 601 to receivea trigger for an aperiodic CSI report as part of an UL grant, from aradio node, in a static DL subframe. The trigger indicates a CSIsubframe set, out of at least two alternative CSI subframe sets. Theexecution of the instructions further causes the UE 600 or arrangement601 to perform an aperiodic CSI measurement for a CSI reference resourcein the indicated CSI subframe set, and to report a result of the CSImeasurement to the radio node, where one of the at least two alternativeCSI subframe sets relates to the one or more static subframes, andanother one of the at least two alternative CSI subframe sets relates tothe one or more flexible subframes, as previously described. The UE 600or arrangement 601 may be configured to report the result of the CSImeasurement to the radio node in a CSI reporting subframe n.

An alternative embodiment of the UE 600 is shown in FIG. 7. FIG. 7illustrates a UE 700, operable in a wireless communication network. Thepart of the UE 700 which is most affected by the adaptation to theherein described method is illustrated as an arrangement 701, surroundedby a dashed line. The UE 700 or arrangement 701 comprises acommunication unit 702 configured to communicate with other entities inwireless communication. The UE 700 or arrangement 701 may further beassumed to comprise further functional units 706, for carrying outregular UE functions.

The UE 700 or arrangement 701 comprises a receiving unit 703, configuredto receive a trigger for an aperiodic CSI report as part of an UL grant,from a radio node, in a static DL subframe. The trigger indicates a CSIsubframe set, out of at least two alternative CSI subframe sets.

The UE 700 or arrangement 701 further comprises a measurement unit 704,configured to perform an aperiodic CSI measurement for a CSI referenceresource in the indicated CSI subframe set. The UE further comprises areporting unit 705, configured to report a result of the CSI measurementto the radio node. The reporting unit 705 may be configured to reportthe result of the CSI measurement to the radio node in a CSI reportingsubframe n.

Radio Node, e.g. BS

Embodiments described herein also relate to a radio node, or BS,operable in a wireless communication system. The radio node isconfigured to perform at least one embodiment of the method performed bya radio node described above. The radio node is associated with the sametechnical features, objects and advantages as the method described aboveand illustrated e.g. in FIG. 5.

Below, an exemplifying radio node 800, configured to enable theperformance of an above described method for handling separate aperiodicCSI reports for one or more static subframes, in which the direction ofsignal transmission is fixed, and one or more flexible subframes, inwhich the direction of signal transmission is flexible, will bedescribed with reference to FIG. 8. The radio node 800 is configured tobe operable in a wireless communication network. The part of the radionode 800 which is most affected by the adaptation to the hereindescribed method is illustrated as an arrangement 801, surrounded by adashed line. The radio node 800 and arrangement 801 are configured tocommunicate with other entities, such as UEs and MME via a communicationunit 802 comprising means for wireless communication and possibly meansfor wired communication. The radio node 800 or arrangement 801 may beassumed to comprise other further functionality 806, for carrying outregular radio node functions, such as scheduling.

The arrangement part of the radio node 800 may be implemented and/ordescribed as follows:

The arrangement 801 comprises processing means 803, such as a processor,and a memory 804 for storing instructions, the memory comprisinginstructions, e.g. computer program 805 which when executed by theprocessing means causes the radio node 800 or arrangement 801 toindicate to a UE, in an UL grant in a static DL subframe, a CSI subframeset, out of at least two alternative CSI subframe sets, in or upon whichthe UE should perform an aperiodic CSI measurement for a CSI referenceresource, where one of the at least two alternative CSI subframe setsrelates to the one or more static subframes, and another one of the atleast two alternative CSI subframe sets relates to the one or moreflexible subframes. The execution of the instructions further causes theradio node 800 or arrangement 801 to receive a CSI report from the UEcomprising a result of the aperiodic CSI measurement in the indicatedCSI subframe set. The radio node 800 or arrangement 801 may beconfigured to receive the CSI report from the UE in a CSI reportingsubframe n.

An alternative embodiment of the radio node 800 is shown in FIG. 9. FIG.9 illustrates a radio node 900, operable in a wireless communicationnetwork. The part of the radio node 900 which is most affected by theadaptation to the herein described method is illustrated as anarrangement 901, surrounded by a dashed line. The radio node 900 orarrangement 901 comprises a communication unit 902 configured tocommunicate with other entities in wireless communication and possiblyalso in wired communication. The radio node 900 or arrangement 901 mayfurther be assumed to comprise further functional units 906, forcarrying out regular radio node functions, such as scheduling.

The radio node 900 or arrangement 901 comprises an indicating unit 903configured to indicate to a UE, in an UL grant in a static DL subframe,a CSI subframe set, out of at least two alternative CSI subframe sets,in or upon which the UE should perform an aperiodic CSI measurement fora CSI reference resource, where one of the at least two alternative CSIsubframe sets relates to the one or more static subframes, and anotherone of the at least two alternative CSI subframe sets relates to the oneor more flexible subframes. The radio node 900 or arrangement 901further comprises a receiving unit 904, configured to receive a CSIreport from the UE comprising a result of the aperiodic CSI measurementin the indicated CSI subframe set. The radio node 900 or arrangement 901may be configured to receive the CSI report from the UE in a CSIreporting subframe n.

The units or modules in the arrangements in the different nodesdescribed above could be implemented e.g. by one or more of: a processoror a micro processor and adequate software and memory for storingthereof, a Programmable Logic Device (PLD) or other electroniccomponent(s) or processing circuitry configured to perform the actionsdescribed above, and illustrated e.g. in FIGS. 4-5. That is, the unitsor modules in the arrangements in the different nodes described abovecould be implemented by a combination of analog and digital circuits,and/or one or more processors configured with software and/or firmware,e.g. stored in a memory. One or more of these processors, as well as theother digital hardware, may be included in a single application-specificintegrated circuitry (ASIC), or several processors and various digitalhardware may be distributed among several separate components, whetherindividually packaged or assembled into a system-on-a-chip (SoC).

The indications or triggers described herein can thus be seen as anaperiodic CSI report request, which term is also used herein.Furthermore, in this disclosure the above terms “a static/flexiblesubframe” are not limited to just one static/flexible subframe butshould be interpreted as at least one static/flexible subframe.

It is to be understood that the choice of interacting units, as well asthe naming of the units within this disclosure are only for exemplifyingpurpose, and nodes suitable to execute any of the methods describedabove may be configured in a plurality of alternative ways in order tobe able to execute the suggested procedure actions. While the solutionhas been described with reference to specific exemplary embodiments, thedescription is generally only intended to illustrate the inventiveconcept and should not be taken as limiting the scope of the solution.For example, the terms “radio node”, “User Equipment, UE”, “staticsubframe”, “flexible subframe”, “trigger”, “CSI report” and “CSImeasurement” have been used throughout this description, although anyother corresponding entities, functions, and/or parameters could also beused having the features and characteristics described here.

It should also be noted that the units described in this disclosure areto be regarded as logical entities and not with necessity as separatephysical entities.

Abbreviations

3GPP Third Generation Partnership Project

CCE Control Channel Element

CoMP Coordinated MultiPoint

CQI Channel Quality Indicator

CSI Channel State Information

DCI Downlink Control Information

DL Downlink

DM RS Demodulation Reference Signal

eNB evolved Node B

(E)PDCCH Enhanced PDCCH

HARQ Hybrid Automatic Repeat Request

ICIC Inter-Cell Interference Coordination

ID Identity

L1 Layer 1

LTE Long Term Evolution

MIMO Multiple Input Multiple Output

PDCCH Physical Downlink Control Channel

PUSCH Physical Uplink Shared Channel

Rel Release

RRM Radio Resource Management

RS Reference Symbol

TDD Time Division Duplex

UE User Equipment

UL Uplink

Below, in an appendix, some alternative solutions to the triggering ofaperiodic CSI will be mentioned.

APPENDIX

An alternative to the explicit signaling or triggering, which is thefocus of this disclosure, could be implicit triggering. For implicittriggering, the aperiodic CSI request can be differentiated for staticor flexible downlink subframes according to any of the followingcriteria:

-   -   The aperiodic CSI report request is carried over uplink grant        for static or flexible uplink subframes; (explained in        Embodiment 1 below)    -   The CCE index of the uplink grant which carries the aperiodic        CSI report request; (explained in Embodiment 2 below)    -   The downlink subframe over which the uplink grant carrying        aperiodic CSI report request is transmitted is special downlink        subframe or not; (explained in Embodiment 3 below)    -   The index of the downlink subframe over which the uplink grant        carrying aperiodic CSI report request is transmitted; (explained        in Embodiment 4 below)    -   The HARQ process ID corresponding to the uplink grant carrying        aperiodic CSI report request; (explained in Embodiment 5 below)    -   The CSI process ID in the uplink grant carrying aperiodic CSI        report request. (explained in Embodiment 6 below)

The above-mentioned criteria will be described in more detail asdifferent embodiments below. In order to realize these embodiments, aradio node or base station is configured to transmit a first trigger fora UE to perform aperiodic CSI reporting for a static subframe, and totransmit a second trigger for a UE to perform aperiodic CSI reportingfor a flexible subframe, just as in the case of explicit triggeringdescribed previously in this disclosure.

Embodiment 1: The Aperiodic CSI Report Request is Carried Over UplinkGrant for Static or Flexible Uplink Subframes

In this embodiment, when a UE receives an uplink grant or a RandomAccess Response grant with a respective CSI request field set to triggera report, the UE is triggered to perform aperiodic CSI reporting basedon whether the UL grant or the Random Access Response grant schedulesPUSCH transmission in the static subframe or flexible subframes. Thismay be realized according to different possibilities:

-   -   If the uplink grant or Random Access Response grant schedules a        PUSCH is transmission in the static uplink subframe, the        aperiodic CSI reporting should involve a CSI measurement in one        or more static downlink subframes. This scheduling thus        corresponds to the first trigger.    -   If the uplink grant or Random Access Response grant schedules a        PUSCH transmission in the flexible subframe, the aperiodic CSI        reporting should involve a CSI measurement in one or more        flexible subframes. This scheduling thus corresponds to the        second trigger.    -   If the uplink grant schedules PUSCH transmissions in both static        and flexible subframes, e.g. UL/DL configuration 0, the        aperiodic CSI reporting should involve CSI measurements in both        static and flexible subframes. This scheduling thus corresponds        to both of the first and second triggers.

Embodiment 2: The CCE Index of the Uplink Grant which Carries theAperiodic CSI Report Request

In this embodiment, a metric can be defined as a function of the indexof the first CCE of the uplink grant which carries the aperiodic CSIreport request. This metric is denoted γ_(cce). In that case, the UEdetermines to report the CSI for the static or flexible downlinksubframes according to predefined rules depending on the metric. As oneexample,γ_(cce)=mod(Ind_(1st) _(_) _(cce)/Agg_(pdcch),2)

Where Ind_(1st) _(_) _(cce) is the index of the first CCE, andAgg_(pdcch) is the aggregation level of the UL grant carrying the CSIreporting trigger. In this embodiment, the UE is triggered to performaperiodic CSI reporting for static and flexible downlink subframes whenthe metric γ_(cce) is 0 and 1, respectively, or when the metric γ_(cce)is 1 and 0, respectively.

Embodiment 3: The Downlink Subframe Over which the Uplink Grant CarryingAperiodic CSI Report Request is Transmitted is a Special DownlinkSubframe or Not

In this embodiment, it may be predefined/configured that a UE candetermine the aperiodic CSI report for the static or flexible downlinksubframes based on the subframe (which may be referred to as a CSIrequest carrying subframe) when the CSI report request received by theUE is a special subframe or not a special subframe.

In this embodiment, the UE may be triggered to perform aperiodic CSIreporting for the static and flexible downlink subframes when the CSIrequest carrying subframe is a special subframe and is not a specialsubframe, respectively, or when the CSI request carrying subframe is nota special subframe and is a special subframe, respectively.

Embodiment 4: The Index of the Downlink Subframe Over which the UplinkGrant Carrying Aperiodic CSI Report Request is Transmitted

As a possibility in this embodiment, the downlink subframes (e.g.including special subframes) which can carry the uplink grant may bedivided into two groups: 1^(st) downlink subframe group and 2^(nd)downlink subframe group. It may be predefined that aperiodic CSI reportrequest carrying over the downlink subframe belonging to the 1^(st) or2^(nd) downlink subframe group triggers the UE to perform aperiodic CSImeasurement for static or flexible downlink subframe, respectively.

As another possibility in this embodiment, another metric can be definedas a function of the subframe index of the CSI request carryingsubframe. This metric is denoted γ_(sub-fn). It may bepredefined/configured by the network that the UE can determine theaperiodic CSI report for the static or flexible downlink subframesaccording to predefined rules. As one example, the metric γ_(sub-fn) maybe defined as:γ_(sub-fn)=mod(subFn,2)

Where subFn is the subframe number or index. In this embodiment, the UEmay be triggered to perform aperiodic CSI reporting for static andflexible downlink subframes when γ_(sub-fn) is 0 and 1, respectively, orwhen γ_(sub-fn) is 1 and 0, respectively.

Embodiment 5: The HARQ Process ID Corresponding to the Uplink GrantCarrying Aperiodic CSI Report Request

As a possibility in this embodiment, the HARQ process IDs can be dividedinto two groups (1st and 2nd). The HARQ process ID corresponding to theuplink grant carrying aperiodic CSI report request belonging to the1st/2nd HARQ process ID group means that the UE should perform theaperiodic CSI report for static/flexible downlink subframes respectivelyor vice versa.

As another possibility in this embodiment, a metric can be defined as afunction of the HARQ process ID corresponding to the uplink grantcarrying the aperiodic CSI report request, and the UE can determine toperform the aperiodic CSI report for static or flexible downlinksubframes according to the predefined rules. As one example, a metricγ_(hp) may be defined as:γ_(hp)=mod(hp_Id,2)

Where hp_Id is the HARQ process identity. In this embodiment, the UE istriggered to perform aperiodic CSI reporting for static and flexibledownlink subframes when γ_(hp) is 0 and 1, respectively, or when γ_(hp)is 1 and 0, respectively.

Embodiment 6: The CSI Process ID in the Uplink Grant Carrying AperiodicCSI Report Request

As a possibility in this embodiment, the CSI process IDs can beassociated with static/flexible downlink subframes. In an example of theembodiment, two sets of CSI process IDs can be defined at the radio nodeor eNB. One set is associated with static downlink subframes, and theother set is associated with flexible downlink subframes. For the CSIprocess associated with static downlink subframes, the correspondingzero-power/non-zero power CSI RS and DM RS may be configured in staticsubframes only, while for the CSI process associated with flexibledownlink subframes, the corresponding zero-power/non-zero power CSI RSand DM RS may be configured in flexible subframes only.

The invention claimed is:
 1. A method performed by a User Equipment, UE,for handling separate aperiodic channel state information, CSI, reportsfor one or more static subframes, in which the direction of signaltransmission is fixed, and one or more flexible subframes, in which thedirection of signal transmission is variable, the method comprising:receiving a trigger for an aperiodic CSI report as part of an uplink,UL, grant from a radio node in a static downlink, DL, subframe, saidtrigger indicating one or more CSI processes and a CSI subframe setrelated to the one or more static subframes; performing an aperiodic CSImeasurement for a CSI reference resource in the CSI subframe set;reporting a result of the aperiodic CSI measurement to the radio node,in a CSI reporting subframe; receiving a second trigger for a secondaperiodic CSI report as part of a second UL grant from the radio node ina second static DL subframe, said second trigger indicating one or moresecond CSI processes and a second CSI subframe set that relates to theone or more flexible subframes; performing a second aperiodic CSImeasurement for a second CSI reference resource in the second CSIsubframe set; and reporting a result of the second aperiodic CSImeasurement to the radio node, in a second CSI reporting subframe. 2.The method according to claim 1, wherein the CSI reference resource isdefined, in the time domain, as a single downlink subframe n-nCQI_ref,where nCQI_ref is an offset such that the single downlink subframe is avalid downlink subframe belonging to the CSI subframe set.
 3. The methodaccording to claim 1, further comprising receiving a configurationchange that changes at least one of the one or more flexible subframes.4. A method performed by a radio node for handling separate aperiodicChannel State Information, CSI, reports for one or more staticsubframes, in which the direction of signal transmission is fixed, andone or more flexible subframes, in which the direction of signaltransmission is variable, the method comprising: indicating to a UserEquipment, UE, in an uplink, UL, grant in a static downlink, DL,subframe, one or more CSI processes and a first CSI subframe set inwhich the UE should perform an aperiodic CSI measurement for a first CSIreference resource, where the first CSI subframe sets relates to the oneor more static subframes; receiving, in a CSI reporting subframe, a CSIreport from the UE comprising a result of the aperiodic CSI measurement;indicating to the UE, in a second UL grant in a second DL subframe, oneor more second CSI processes and a second CSI subframe set in which theUE should perform a second aperiodic CSI measurement for a second CSIreference resource, where the second CSI subframe sets relates to theone or more flexible subframes; receiving, in a second CSI reportingsubframe, a second CSI report from the UE comprising a result of thesecond aperiodic CSI measurement.
 5. The method according to claim 4,wherein the CSI reference resource is defined, in the time domain, as asingle downlink subframe n-nCQI_ref, where nCQI_ref is an offset suchthat the single downlink subframe is a valid downlink subframe belongingto the CSI subframe set.
 6. The method according to claim 4, furthercomprising indicating to the UE a configuration change that changes atleast one of the one or more flexible subframes.
 7. A User Equipment,UE, for handling separate aperiodic channel state information, CSI,reports for one or more static subframes, in which the direction ofsignal transmission is fixed, and one or more flexible subframes, inwhich the direction of signal transmission is variable, the UEcomprising a processor, the processor configured to perform operationscomprising: receiving a trigger for an aperiodic CSI report as part ofan uplink, UL, grant from a radio node in a static downlink, DL,subframe; said trigger indicating one or more CSI processes and a CSIsubframe set related to the one or more static subframes; performing anaperiodic CSI measurement for a CSI reference resource in the CSIsubframe set; reporting a result of the aperiodic CSI measurement to theradio node in a CSI reporting subframe; receiving a second trigger for asecond aperiodic CSI report as part of a second UL grant from the radionode in a second static DL subframe, said second trigger indicating oneor more second CSI processes and a second CSI subframe set that relatesto the one or more flexible subframes; performing a second aperiodic CSImeasurement for a second CSI reference resource in the second CSIsubframe set; and reporting a result of the second aperiodic CSImeasurement to the radio node, in a second CSI reporting subframe. 8.The User Equipment according to claim 7, wherein the CSI referenceresource is defined, in the time domain, as a single downlink subframen-nCQI_ref, where nCQI_ref is an offset such that the single downlinksubframe is a valid downlink subframe belonging to the CSI subframe set.9. The User Equipment according to claim 7, further comprising:receiving, from the radio node, a configuration change that changes atleast one of the one or more flexible subframes.
 10. A radio node forhandling separate aperiodic Channel State Information, CSI, reports forone or more static subframes, in which the direction of signaltransmission is fixed, and one or more flexible subframes, in which thedirection of signal transmission is variable, the radio node comprisinga processor, the processor configured to perform operations comprising:indicating to a User Equipment, UE, in an uplink, UL, grant in a staticdownlink, DL, subframe, one or more CSI processes and a first CSIsubframe set in which the UE should perform an aperiodic CSI measurementfor a first CSI reference resource, where the first CSI subframe setsrelates to the one or more static subframes; receiving, in a CSIreporting subframe, a CSI report from the UE comprising a result of theaperiodic CSI measurement; indicating to the UE, in a second UL grant ina second DL subframe, one or more second CSI processes and a second CSIsubframe set in which the UE should perform a second aperiodic CSImeasurement for a second CSI reference resource, where the second CSIsubframe sets relates to the one or more flexible subframes; receiving,in a second CSI reporting subframe, a second CSI report from the UEcomprising a result of the second aperiodic CSI measurement.
 11. Theradio node according to claim 10, wherein the CSI reference resource isdefined, in the time domain, as a single downlink subframe n-nCQI_ref,where nCQI_ref is an offset such that the single downlink subframe is avalid downlink subframe belonging to the CSI subframe set.
 12. The radionode according to claim 10, wherein the operations further compriseindicating to the UE a configuration change that changes at least one ofthe one or more flexible subframes.